1. Field of the Invention
The invention relates broadly to refrigeration and preferably to a refrigeration method using a non-aqueous, non-hydrocarbon refrigerant to contact a hydrocarbon composition as discussed below.
2. Description of Related Art
Common refrigeration systems include vapor compression, fan, heat exchange and absorption systems. Low temperature or cryogenic processes have also become popular, due in part to the increased demand for air liquefaction and separation capacity to make liquid products such as liquid oxygen and liquid nitrogen and also for the low temperature separation of natural gas and natural gas products. Methods typically used to achieve cryogenic temperatures include vaporization of liquids, Joule-Thomson expansion and expansion of gases in an engine doing external work such as a turbo expander.
A mechanical refrigeration cycle is a reversed heat engine system. Generally, vapor compression systems use a pressurized hydrocarbon heat transfer media as a refrigerant. The pressure on the refrigerant is lowered, usually by expansion across a valve. The refrigerant then flows to an evaporator where heat is absorbed, vaporizing the hydrocarbon. The vaporized refrigerant is then compressed and condensed to begin the cycle again. The chemical processing and refining industries are major users of mechanical refrigeration.
Refrigeration is typically used in the chemical processing and refining industries to remove the heat produced by reactions used to make products and to separate components by condensation, distillation or crystallization. Refrigeration systems are also used to process, store and transport perishable foods. Lastly, refrigeration is used to air-condition buildings and cars.
There are many disadvantages associated with current refrigeration designs and methods. Many refrigeration systems are limited by the temperature of the refrigerant. For vapor compression systems, the lowest attainable temperature of the refrigerant is typically determined by its composition, its associated properties and the selected operating pressure. Ambient air conditions, including temperatures and relative humidity, may limit refrigeration produced by air coolers such as fin fans and cooling towers. Absorption systems exhibit another disadvantage similar to that of the vapor compression systems limitations in that the selected operating pressure, e.g., the vacuum, coupled with the brine selection for the absorption system, indirectly result in temperature limits. At higher vacuums, the vaporization temperature drops for a given brine composition. Once the vacuum level is determined, for a given brine composition, the vaporization temperature is established. These temperature limits result in limited refrigeration available, condenser capacity limits and purity limits on products.
Accordingly, a continuing need exists for overcoming these temperature limitations or indirect temperature limitations as reflected by system pressure or ambient conditions. Also, the art has sought a method for refrigeration which does not require the use of excessively large heat exchanger areas or relatively large capacity compressors or vacuum pumps to overcome processing capacity limitations and product purity limitations. Accordingly, the present invention relates to a method of improved refrigeration which may result in reduced energy costs by lowering reflux requirements, by improving separation, and by decreasing or eliminating flooding in distillation columns. In another aspect of the invention, lowered energy requirements for reboiling distillation columns may result from increasing vaporization of light hydrocarbons by introducing a non-hydrocarbon vapor to a hydrocarbon liquid phase, lowering the temperature of the liquid and vapor and reducing light hydrocarbon losses, particularly of ethane or ethylene.